1. Field of the Invention
The present invention relates to data storage systems that use removable data storage media. More particularly, the invention includes a data backup system that employs multiple storage drives for accessing removable data storage media, where idle data storage media are analyzed and selectively demounted to increase availability of the storage drives and also minimize unnecessary mount/demount operations.
2. Description of the Related Art
With the increasing importance of electronic information today, there is a similar increase in the importance of reliable data storage. The market abounds with different means of data storage today, ranging from high-speed, more expensive products such as random access memory (RAM), to slower speed, less expensive products such as magnetic tape. Once consumers recognize the importance of reliably storing data, many also recognize the critical value of backup storage, in case the stored data is lost through accident, device failure, catastrophe, etc.
Magnetic tape is one of the most popular types of backup storage media because of its large storage capacity and affordability. In the early days of backup technology, magnetic tape backup operations were performed in xe2x80x9cbatchxe2x80x9d style. Namely, the tape storage system was loaded with one or more tapes in the late evening or another convenient backup time, and the storage system was invoked to copy all source data to tape backup.
More recently, consumers have favored xe2x80x9cevent-drivenxe2x80x9d backups, which are backups of smaller datasets performed during ongoing operation of the storage system instead of consolidating backup operations at pre-arranged xe2x80x9cbatchxe2x80x9d times. Event-driven backups are triggered by particular events, such as arrival of a particular time, commencement of a data storage transaction, user request, or any other pertinent storage or processing event. One example of an event-driven backup is a periodic auto-save operation. Another example is the backup storage of a bank account record before completing a new transaction, in order to preserve the ability to restore the bank account record to its previous state in case that new transaction fails. In some cases, event-driven backups are achieved using a single tape mounted to a single tape drive. In other cases, larger event-driven backups can be performed by storing data to multiple tapes in parallel, by using multiple tape drives concurrently.
Unlike batch backups, where the storage system is copied en masse during a lengthy backup session, event-driven backups present greater challenges from the standpoint of tape management. Particularly, tapes can reside in their tape drives for a long time because backup data arrives relatively slowly, making it difficult to completely fill a tape. Event-driven backup requests also present a bursty, unpredictable data arrival pattern that can make planning difficult.
Another challenge with event-driven backups is minimizing mount/demount overhead. If tapes containing a backup dataset are already mounted when a backup event occurs, the backup can be performed without any mount/demount overhead. Therefore, there is some incentive to leave tapes mounted where possible. However, if tapes are permitted to remain mounted after use, and the next backup event does not concern these tapes, additional overhead is incurred by having to mount the proper tapes.
Accordingly, backup storage engineers are faced with numerous tape management challenges. Decisions must be made as to which tapes to demount and which tapes to leave mounted in order to provide the most efficient possible backup strategy. One consequence of an efficient backup strategy includes the cost of having a human or machine operator perform an excessive number of tape mounts and demounts. Inefficient backup strategies can also frustrate storage system users with delays that occur while backup tapes are located and mounted.
There have been some previous approaches to the problems presented by event-driven backups. One such approach accumulates backup data in a magnetic disk drive storage queue, and then offloads the backup data to tape in response to demand, time schedule, etc. Another approach accumulates backup data in a circuit memory queue, and then downloads memory to tape whenever an entire tape""s worth of data has accumulated in memory. The foregoing approaches have certain advantages from the standpoint of minimizing tape mount-demount operations. However, these techniques increase hardware costs by requiring additional disk drive or memory storage. Also, these techniques may not provide adequate disaster protection for some applications, since they are acutely vulnerable to the failure of the disk drive or memory storage queues.
Consequently, due to these and other unsolved problems, the state of the art in event-driven backup technology may not be completely satisfactory for some applications. Moreover, engineers at International Business Machines Corp. (IBM) are continually seeking improvements in the performance and efficiency of tape backup systems.
The present invention is implemented in a data backup system that employs multiple storage drives for accessing removable data storage media, where idle data storage media are analyzed and selectively demounted to increase availability of the storage drives and also minimize unnecessary mount/demount operations. The backup system is initialized by establishing a maximum number of permissible concurrently mounted idle storage media, and also establishing a maximum time for leaving idle storage media mounted. After initialization, storage media mounted to the media drives are analyzed for possible demounting. The system determines how many storage media are presently mounted, and each media""s mount time. Then, the system identifies suitable demounting candidates (if any) to comply with the established maximums of concurrent mounts and mounting time. Namely, the system identifies the media with the greatest mount times whose demounting is necessary to both (1) reduce the number of concurrent mounts down to the maximum number, and (2) demount any storage media with excessive mount times. Advantageously, the maximum number of concurrent mounts and the maximum idle time may be adjusted xe2x80x9con the fly,xe2x80x9d such that the system recognizes and promptly honors the new parameters. As another additional feature, storage media with excessive idle mount times may be logically interchanged with emptier storage media, where the emptier storage media is demounted instead of the media with excessive idle mount time. This helps to thoroughly fill older storage media with data, avoiding premature and costly utilization of new, empty storage media.
The foregoing features may be implemented in a number of different forms. For example, the invention may be implemented to provide a method of operating a backup data storage system, as discussed above. In another embodiment, the invention may be implemented to provide an apparatus such as a backup data storage system. In still another embodiment, the invention may be implemented to provide a signal-bearing medium tangibly embodying a program of machine-readable instructions executable by a digital data processing apparatus to operate a backup data storage system as shown herein. Another embodiment concerns logic circuitry having multiple interconnected electrically conductive elements configured to operate a backup data storage system as depicted herein.
The invention affords its users with a number of distinct advantages. For example, the invention avoids excessive mount/demount operations by carefully analyzing characteristics of the presently mounted storage media. Moreover, the invention encourages faster completion of storage operations for a number of different reasons. First, the invention increases the likelihood that some storage drives are available for new media, since the number of concurrent mounts is limited to a maximum number. Second, the invention increases the likelihood that required storage media are already mounted to storage drives and ready to conduct read/write operations because the less-idle media are retained and more-idle media are demounted. Additionally, the invention supports disaster recovery by promptly writing data to tape backup rather than pooling data in a vulnerable, intermediate storage media such as circuit memory or disk drive storage. The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.